Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
	Home All data for one species Geometry Experimental Experimental Geometries Same bond/angle many molecules Internal Coordinates by type Bond angles Calculated Calculated geometry Rotational constant Moments of inertia Products of moments of inertia BSE Bond lengths Show me a calculated geometry Comparisons Bonds, angles Rotational Constants Products of moments of inertia Point group Bad Calculations Bad moment of inertia Tutorials and Explanations Angle formulas Vibrations Experimental Vibrational frequencies Calculated Frequencies Scale factors Reactions Entropies Ions List Ions Energy Calculated Ionization Energy Compare Ionzation energy Electron Affinity Calculated Electron affinity Compare Electron affinity Proton Affinity Calculated Proton affinity Compare Proton affinity Ionization changes point group Experimental One molecule all properties One property a few molecules Enthalpy of formation Entropy Integrated Heat Capacity Heat Capacity Rotational Constants Vibrational Frequencies Dipole moment Ionization Energy Polarizability Quadrupole Point Groups Geometry Experimental Geometries Internal Coordinates by type Bond angles Rotational Constants Point Groups Diatomic bond lengths Vibrations Vibrational frequencies Diatomic Triatomics Energy Atomization Energy Internal Rotation Electrostatics Dipole Quadrupole Polarizability Reference Data Reference states Spin Splittings Molecules with good enthalpy Enthalpy at 0 Kelvin Calculated Energy Optimized Energy Energy 298K Minimum conformation Hydrogen bonds H bond with counterpoise Reaction Reaction Energy 0K Reaction Energy 298K Internal Rotation Barriers to internal rotation Rotational barrier and dipole Rotational Barrier 2 molecules Orbital HOMO LUMO gap HOMO Orbital Energies Nuclear repulsion energy Correlation Full vs Frozen core energies Partial correlation energies Ion Calculated Ionization Energy Vertical ionization Energy Calculated Electron affinity Calculated Proton affinity Atom charge differences Excited State Singlet triplet gap Electronic state Transition state Basis Set Extrapolation BSE energy BSE Bond lengths Geometry Calculated geometry AIM bond orders One type of bond Rotation Rotational constant Products of moments of inertia Moments of inertia Inertial defects Second moments Point group State symmetry <r2> Sorted by r2 Z-matrix Bad Calculations Bad moment of inertia Bad Calculated Bond Lengths Bad point group Worst molecules Vibrations Frequencies Animated vibrations Anharmonic Zero point energy (ZPE) Scale Factors Scale factors Scale factor uncertainty Calculate a scale factor Why scale vibrations Set scaling factors Bad Calculations Bad Vib. 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Big anharmonicity Electrostatics Charges Mulliken CHELP Aim ESP Dipole Dipole Dipole angle Dipole calculation types Quadrupole Polarizability Spin Spin density Entropy and Heat Capacity Entropy Reaction entropy Heat Capacity Reaction Reaction Energy 0K Reaction Energy 298K Isodesmic reactions Transition State Transition state Transition state frequencies Transition state geometries IRC Lookup by property By frequency Comparisons Geometry Bonds, angles Bond, angle, or dihedral DFT grid size on point group DFT grid on bond length Core correlation - bond length Same bond/angle many molecules Isoelectronic diatomics Isoelectronic triatomic angles Average bond lengths Rotation Rotational Constants Products of moments of inertia Point group Vibrations Vibrations 2 calculations Frequency differences One frequency Zero point energy Intensity Intensity for one mode Vibrational intensities Reduced mass comparison Anharmonic Triatomic Scale factors Energy Reaction Reaction Energy 0K Reaction Energy 298K Atomization 0K Atomization 298K Single point vs optimized DFT grid size on energy Semiempirical enthalpy Internal rotation Similar molecules Conformation Sets of isomers Sets of tautomers Isomers Entropy Entropy Heat capacity Entropy of several molecules Integrated heat capacity Reaction entropy Electrostatics Dipole Polarizability Several molecules Quadrupole Ion Compare Ionzation energy Koopman ionization energy Koopman IE for a few molecules Compare Electron affinity Compare Proton affinity Protonation Site Resources Info on Results Calculations Done Method and basis set List molecules One molecule Multiple conformers, states Multiple conformers, states Basis functions used I/O files Input/output files MOL file Z-matrix wfn files Glossary Conversion Forms B to I, I to B Angle formulas Integrated heat Capacity Calculating Enthalpy Links NIST Links NIST webbook bibliographic data CCCBDB Experimental data External links Basis Set Exchange Computational Chemistry List Thermochemistry in Gaussian Minnesota Database Collection Benchmark Energy and Geometry Point Groups Thermochemistry Thermochemistry Molecules with good enthalpy A → B + C Reference states Tutorials Vibrations Why scale vibrations Zero-point energies Entropy Methyl rotor entropy Entropy and conformations Energy Getting enthalpy of formation Vertical vs adiabatic IE Thermo from calculations Electrostatics Dipole parts by point group Quadrupoles Geometry Angle formulas Cost Cost Comparison Timings Comparison Bad Calculations Geometry Bad moment of inertia Bad Calculated Bond Lengths Bad point group Worst molecules Vibrations Bad vib. Calc. vs exp. Bad Vib. HF vs MP2 Bad scale factors Low excited states Oddities NaCN Is not linear FAQ Help Units Choose Units Energy Bond length Rotational Constant Moment of Inertia Dipole and Quadrupole Polarizability Explanations Hartree cm-1 Debye Credits Just show me Show me a calculated geometry Summary Using older interface Limit Basis sets Method options List Recent molecules Choose a few Molecules Number of atoms By heavy atoms Diatomics InChI Deuterated Dimers Geometry Point group Point group count Bonds types Isodesmic reactions Bad point group Multiple conformers, states Vibrations Big anharmonicity Energy Enthalpy at 0 Kelvin Similar molecules Similar Isomers Cis/trans Tautomers Multiple conformers, states Ions, Dipoles, etc. List Ions Ionization changes point group Dipole Quadrupole Polarizability Proton Affinities Index of CCCBDB Feedback Error form Wants
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Summary of the CCCBDB

The goals are:

1) Provide a benchmark set of molecules for the evaluation of ab initio computational methods.

2) Allow the comparison between different ab initio computational methods for the prediction of thermochemical properties.

The thermochemical values with error bars included in the CCCBDB are:

1. Enthalpies of formation.

2. Entropies, heat corrections (integrated heat capacity).

3. Data needed to compute thermochemical properties, such as geometries, rotational constants, vibrational frequencies, barriers to internal rotation, and electronic energy levels.

4. Additional computed properties such as atomic charges, electric dipole moments, quadrupole moments, polarizabilities, and HOMO-LUMO gaps. See the index (Section XIX. Index of Properties) for more properties.

The molecules to be included have been selected from previous collections, such as the G2 data set [Larry A. Curtiss, Krishnan Raghavachari, Gary W. Trucks et al., JCP 94 (11), 7221 (1991)] and the G2 extended data set [Larry A. Curtiss, Krishnan Raghavachari, Paul C. Redfern et al., J. Chem. Phys. 106 (3), 1063 - 1079 (1997)]. This set has been augmented from the NIST Chemistry Webbook using the following criteria:

The error bars on the Enthalpy of formation are less than or equal to 8 kJ/mol.

The species contains no atoms with atomic number greater than 35 (bromine). Except there are a few molecules containing Iodine. We are slowly adding a few molcules containing the first-row transition metals.

The species contains six or fewer heavy atoms and twenty or fewer total atoms. This allows species as large as hexane.

The above constraints have been loosened to include some larger species (substituted benzenes, cyclooctatetraene, S₈, naphthalene, adamantane)

See sections I.B.1.b or I.B.1.c for lists of the molecules sorted by number of atoms or by number of heavy atoms.

1. CODATA [J. D. Cox, D. D. Wagman, and V. A. Medvedev, CODATA Key values for Thermodynamics (Hemisphere, New York, 1989)] This is a short list of species with internationally accepted values for enthalpies of formation, entropies and heat corrections. Provides error bars for all three properties.
2. JANAF [M. W. Chase, Jr., C. A. Davies, J. R. Downey, Jr. et al., Journal of Physical and Chemical Reference Data 14 Supplement No. 1 (1985)] This is an evaluated list of mostly inorganic species. Provides error bars for enthalpies and entropies.
3. Gurvich [L. V. Gurvich, I. V. Veyts, and C. B. Alcock, Thermodynamic Properties of Individual Substances (Hemisphere Publishing Corporation, New York, New York, 1989)] Evaluated. Small organics. Error bars for enthalpy.
4. TRC [Michael Frenkel, G. J. Kabo, K. N. Marsh et al., Thermodynamics of Organic Compounds in the Gas State (Thermodynamics Research Center, College Station, Texas, 1994)] Evaluated. No error bars.
5. Other sources on individual species where noted.

GENERAL NOTES

General discrepancy between measured and calculated data.

1. Enthalpies of formation are not measured. The properties determined experimentally are usually Enthalpies of reaction at some temperature above 0 K. The ab initio methods provide an absolute energy (relative to compete ionization of all atoms) at 0 K. To convert from one temperature to another, one uses the integrated heat capacity (heat correction). Ideally the procedure and supporting data used to convert from the experimental measurement to a Enthalpy of formation would be available in the database. This is true for the ab initio determinations as well, where the simplest property to calculate is the atomization energy of a molecule at 0 K.

Interconnectedness of data.

1. Geometries are needed to determine rotational constants, which are needed for heat corrections and entropies. Geometries are also useful as starting input for ab initio calculations. Experimental geometries can be compared with ab initio geometries to evaluate ab initio methods.

2. Vibrational frequencies are needed for heat corrections and entropies.

3. Some Enthalpies of formation are derived from measured equilibrium, this derivation requires an entropy. If the vibrational frequencies come from ab initio methods, the Enthalpy of formation is not purely an experimental measurement.

Lack of experimental data

1. The integrated heat capacity, or heat correction, is used to convert the enthalpy of formation from one temperature to another. It is calculated using standard statistical mechanics, using information such as mass, rotational constants, vibrational energy levels, and electronic energy levels. These have been experimentally determined in some cases, but not all. Ab initio methods can provide rotational constants and vibrational energy levels. Many of the errors for the integrated heat capacity obtained from ab initio calculations come from ignoring spin orbit splitting in open-shell linear molecules or ignoring low lying electronic states and errors in the vibrational energy levels for non-harmonic vibrations. They can amount to ≈1kJ/mol. The errors in entropies obtained from calculations arise from the same sources and can amount to ≈10 J/mol K (so @ 300 K ≈3kJ/mol)